Coal contributes a large percentage of the electricity generation in the world today and is expected to maintain its dominant share in the foreseeable future. Nonetheless, significant environmental pressures have led to the development of emission reduction systems to meet every increasing environmental demands. As a result, plant designs have had to meeting the contradictory requirements of high efficiency operation at reduced CO2, SO2, NOx, emission levels.
A particular advantageous plant arrangement arising out of these developments is the Oxy-combustion steam plant with CO2 capture. Rather than operating an air combustion system, the system uses oxygen, usually produced in an air separation unit for the combustion of the primary fuel. Oxy-combustion processes produce flue gas typically having CO2, water and O2 as its main constituents wherein the CO2 concentration is typically greater than about 70% by volume. The high concentration of CO2 enables relatively simply CO2 Capture in a Gas Processing Unit.
A typical arrangement of an oxy-combustion capture plant includes several pre CO2 extraction purification steps. These may include an Electrostatic Precipitator for removing particulate matter, a Flue Gas Desulfuriser for removing sulphur, and a Flue gas condenser for water removal. For reasons of thermal efficiency, a Flue Gas Heat Recovery System may additionally be located between the Electrostatic Precipitator and Flue Gas Desulfuriser.
An example of a typical water steam cycle of a high efficiency oxy-combustion steam plants is shown in FIG. 1. The plant comprises a triple-pressure series of reheat steam turbines HP, IP. LP fed by steam from a boiler 42. Exhaust steam from the last low pressure steam turbine LP is condensed in a condenser 2 before being polished 4 and pumped 3 successively through a series of low pressure heater 6, 7, 8, 9, 31, a feed water tank 36 and high pressure heaters 32 before returning to the boiler 42 in a closed loop. The heat source for the low and high pressure heaters is typically steam extracted from the low/intermediate and high pressure steam turbines.
Due to the large benefit in ensuring the highest efficiency cycle there is a continuing need to find ways of better integrating the thermal sinks of the oxy-combustion capture systems within the steam power plant. This requires an optimization of the heat sinks of the capture systems with the plant cycle to ensure no energy is wasted. In particular, this needs consideration of how to integrate the Air Separation Unit, Flue Gas Heat Recovery System, Flue Gas Condenser and Gas Processing Unit into the steam cycle.